Method and apparatus for prescription application of products to an agricultural field

ABSTRACT

A prescription farming control system includes a navigation controller and a product delivery controller for controlling the rate of operation of a number of agricultural product delivery mechanisms mounted on an applicator vehicle as a function of the global position of the vehicle in an agricultural field. Information is stored in computer memory on board the vehicle to define a number of layers corresponding to each of the delivery mechanisms, each layer including a number of zones representing different levels of activity of the corresponding mechanism. Each zone is defined by a plurality of vertices, rather than on a pixel-by-pixel basis. The navigation controller receives satellite positioning data to combine with pseudorange correction data received from a fixed ground station to determine a corrected accurate global position of the vehicle. A graphics coprocessor includes active invisible graphics memory page onto which each layer is sequentially drawn and interrogated. One user selected layer can be stored on an inactive visible graphics memory page for visual display and then page flipped to the active page for subsequent interrogation. The pixel on each layer associated with the current global position of the vehicle is interrogated to determine the proper level of activity of the delivery mechanism at that location. The product delivery controller includes features to prevent re-application of a product on portions of the agricultural field over which the vehicle has already traveled.

BACKGROUND OF THE INVENTION

The present invention concerns a method and apparatus for controllingthe manner of operation of functional devices based upon navigationalinput. Such a method and apparatus is particularly useful in theapplication of chemical products, such as fertilizer, to agricultural orfarm land. More specifically, the invention contemplates a method andapparatus for prescription application of these agricultural products tothe land wherein specific chemical blends are applied in accordance withthe needs of various soil types and crops.

It is known in the agricultural art that a given tract of agriculturalland, or a field, possesses variable characteristics that relate andcontribute to crop fertility. The presence of different soil types andexisting soil constituency levels contribute to this variability.Certain areas of a field will require different farming inputs, such aspesticides, nutrients and irrigation, than other areas of the samefield. The practice of matching inputs with crop soil requirements hascome to be known as "prescription farming". In general, the focus ofprescription farming on varying the application rates of farming inputsfrom point to point within a field, rather than using a single, averagerate over the entire field. The goal of prescription farming is tosupply crops with only the inputs that they require, and no more, toprovide maximum yields.

For decades, farmers have practiced prescription farming by manuallyapplying additional inputs in specific areas of a given field where thefarmer knew from experience (and often trial and error) that suchadditional inputs were needed. Such manual application of inputs isrelatively inaccurate and unscientific.

Attempts have also been made to mechanize the process of prescriptionfarming. To this end, there are applicator vehicles currently on themarket equipped with systems to allow application of varying ratesand/or combinations of inputs. Such variable applicator vehicle systemsare equipped with electronic product delivery controllers which signalthe system pumps and/or motors to vary the rates of application of thevarious inputs carried on board the vehicle. These variable rateapplicator vehicles help to increase the accuracy of application.However, the problem still remains with these systems of navigatingthrough the field. Although a farmer can determine and vary the rate ofapplication of a particular input, the accuracy of the prescriptionfarming process is questionable if the farmer cannot precisely determinehis position in the field during the application process as theapplicator vehicle is moving.

To this end, attempts have been made to increase the accuracy of theprescription farming process by generating computer-readable maps thatset forth prescriptions on a field-by-field basis. This approachcontemplates a computer mounted on the applicator vehicle whichinterfaces with electronic product delivery controllers which controlthe various input pumps and motors. Although these approaches have takensteps toward more accurate prescription farming, several inadequaciesremain.

First, current methods of mechanizing prescription farming use deadreckoning as a navigation method to determine the position of theapplicator vehicle as it moves through the field. This means that theposition of the vehicle is based at all times on its relation to a fixedstarting position. The vehicle's relative position in the field is afunction of a predetermined (rather than actual) speed and the vehicletravel time to determine a distance as measured from the fixed startingposition. One drawback of this approach is that the vehicle must bedriven at a fixed speed that has been previously provided to theon-board computer. Another drawback is that the vehicle must be drivenin fairly straight and parallel lines through the field, often requiringsuperior driving skills on the part of the vehicle operator. Moreover,with this approach, the application process must be put on stand-by whena turn is made at the end of the field, otherwise the dead reckoningsystem will incorrectly determine that the vehicle is farther along inthe field than its true position justifies. If the vehicle operatorbegins at the wrong point in the field, drives in the wrong direction,fails to maintain a straight driving path, or forgets to put the systemin a stand-by mode during a turn, the application process will fail inits essential purpose because inputs will be applied at improperlocations on the field. With this prior art dead reckoning approach,even the slightest operator oversight or error can result in improperapplication of input products to the field.

Second, current mechanized prescription farming methods require datacontained on the digital prescription map to be reduced to a relativelysmall number of variables. Four example, if a given field requires tenrate variations of six inputs, or products, one million possibleapplication combinations result. Prior digital prescription farmingtechniques are not capable of storing this much information, and insteadare limited to about five variations for up to six different products.This severe restraint prohibits effective prescription determination andgeneration, as well as effective data management within the on-boardcomputer.

Third, current mechanized prescription farming methods require fieldmaps to be generated in a raster format in which each pixel on thecomputer monitor is assigned a discrete digital value representative ofthe soil type at the location of the field represented by the pixel.This protocol severely limits the size of the field that can berepresented or contained on a single map while still maintainingaccuracy.

In short, prior computer-based mechanized prescription farming systemshave required excessive operator input with little room for human error.In addition, these systems are often unwieldy in their implementation,even with digital computer technology.

SUMMARY OF THE INVENTION

The present invention contemplates a method and apparatus to act as anavigation controller for interfacing with electronic product deliverycontrollers on a farming input applicator vehicle. The invention derivesthe navigation information using the global positioning system (GPS).

Specifically, the invention uses differential, kinematic GPS todetermine the precise global position of the applicator vehicle in anagricultural field. A computer system reads farming input prescriptioninformation, interprets this information, and sends appropriateinstructions to the product delivery controllers as a function of theglobal position of the vehicle in the field. The farming inputprescription information is preferably made available to the computersystem on a solid state battery backed random access memory (RAM) orelectrically erasable programmable read only memory (EEPROM) disk.Prescription boundary information is provided in a vector format inglobal, real-world coordinates, such as latitude and longitude(lat-lon). Each prescription area, referred to as a "zone", isdifferentiated according to a user-assigned color scheme.

The prescription data is arranged so that each input or product isrepresented by a "layer", each layer in turn containing several zonescorresponding to a specific rate of application of the product. Forexample, a first layer might represent potash which can be applied atten different rates within a given field. In accordance with the presentinvention, a digital map of the field includes one layer assigned topotash that is segmented into ten zones, each represented by a differentcolor. A second layer might represent the input/product potassium forwhich only three different application rates are required within thefield. Thus, the digital map would include a separate defined layer forpotash having only three zones. It can be seen that in accordance withthe present invention, prescription data for a field is represented by adigital map containing multiple layers, each representing a separateproduct/input, each layer containing multiple zones representingdifferent rates of application of the particular product.

Components of the computer system of the present invention are mountedin the applicator vehicle and interfaced to electronic product deliverycontrollers of the vehicle. As the vehicle is driven through the field,the on-board computer components determine the position of the vehiclein the field using data obtained from vehicle mounted GPS receivingequipment. Software within the on-board computer accesses theprescription information contained in the solid state memory andanalyzes each layer of the digital map to determine the application ratefor each product required for the specific position of the vehicle, andthen instructs the product delivery controllers accordingly.

Since the present invention uses real-world coordinates (lat-lon) todefine the position of the vehicle on the field, there is no need forthe required fixed starting point, scheduled drive pattern for theapplicator vehicle or stand-by mode to perform a turn at the end of thefield. In addition, the on-board computer of the invention records theglobal coordinates over which the vehicle has already traveled andautomatically prevents the application of product over an area more thanonce, thereby eliminating the dangers of over-application present withprior systems. A display monitor in the cab of the applicator vehicleincludes a display of the agricultural field with an icon or symbolrepresenting the location of the vehicle. In one aspect, the vehiclesymbol always remains in the center of the map display. Moreover, theinvention contemplates capabilities to "zoom" in and out on the fielddisplay, thereby eliminating field size constraints.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of an agricultural field positionedwithin a tract of farm land.

FIG. 2 is a top view of an applicator vehicle for use with the presentinvention with the navigation controller and product delivery controllerof the invention represented schematically.

FIG. 3 is a schematic representation of the components of the presentinvention which implement the differential navigation techniques of theinvention.

FIG. 4 is a block diagram depicting the basic components of theapparatus of the present invention.

FIG. 5 is a pictorial representation of the( display console used withthe apparatus of the invention with a portion of a field map displayedthereon.

FIG. 6 is a flowchart of the main procedure implemented by software inaccordance with the present invention.

FIG. 7 is a flowchart of the mass storage loading procedure implementedby software in accordance with the present invention.

FIG. 8 is a pictorial representation illustrating the multiple layer mapprotocol implemented by software in accordance with the presentinvention.

FIG. 9 is a chart illustrating the matrix of map layers and zonesimplemented by software in accordance with the present invention.

FIG. 10 is flowchart of the map generation procedure implemented bysoftware in accordance with the present invention.

FIG. 11 is a pictorial representation of two map displays on the displayconsole illustrating the moving map feature implemented by software inaccordance with the present invention.

FIG. 12a is a graphical depiction of the protocol implemented bysoftware for translating polygons representing zones within a map layer.

FIG. 12b is a graphical depiction of the protocol implemented bysoftware for rotating polygons representing zones within a map layer.

FIGS. 13a and 13b are pictorial representations of two menus displayedon the display console and generated by software in accordance with thepresent invention.

FIG. 14a is a pictorial representation of a map display on the displayconsole illustrating the zoom feature implemented by the software of thepresent invention.

FIG. 14b is a pictorial representation of a map display on the displayconsole illustrating a feature implemented by software of the presentinvention which permits navigation to a field to be farmed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The environment for use of the present invention is depicted first inFIG. 1. Specifically, FIG. 1 represents a tract of land, with afarmhouse or equipment storage facility F showing at one corner of thetract of land. The tract of land also includes acreage A to be treatedby the farmer, namely a growing field which is to be treated withcertain agricultural products and chemicals. The acreage A can include apond P and a number of treatment prescription areas A₁ -A₅. In a morerudimentary form, the areas A₁ -n represent regions of different soiltypes. For instance, these regions can correspond to soils havingdifferent moisture retention capabilities or moisture content. Thespecific soil composition for each of these regions can then beintegrated into a System for determining a prescription to be applied tothe field based upon the particular crops to be grown and thecharacteristic of the soil at the various locations in the acreage A.

Referring now to FIG. 2, a spreading apparatus or applicator vehicle 10is depicted which is used in connection with the present invention. Inparticular, the vehicle 10 can include a number of product bins11_(a-f). Each of the bins may contain a variety of agricultural bulkproducts, such as granular fertilizers. In addition, the vehicle 10includes a pair of liquid tanks 12_(a) and 12_(b) which can be used tocarry liquid herbicides or insecticides, for example. Further, a pair ofaccessory bins 13_(a) and 13_(b) can also be provided for additionalgranular micronutrients. The contents of each of the bins and liquidtanks is fed to a rotary spreader 15 which dispenses the agriculturalproducts onto the field. The product is discharged from each of the bins11_(a-f) by way of a corresponding rotary feeder 17_(a-f). The feeder isdriven by a motor 18_(a-f) which is itself commanded by a controller19_(a-f).The bulk product dispensed from each of the bins is fed onto aproduct conveyor 20 which conveys the product down to the rotaryspreader 15. The conveyor 20 is driven by a separately controllablemotor 21.

Product is dispensed from the liquid tanks 12_(a) and 12_(b) by way of acorresponding pump 22_(a), 22_(b) through a corresponding line 23_(a),23_(b) to the location of the rotary spreader 15. The accessory bins13_(a-b) also include corresponding rotary feeders 24_(a-b), motor25_(a-b) and motor controller 26_(a-b).

The applicator vehicle 10 also includes an on-board system controller 30which ultimately provides signals to each of the controllers for each ofthe product dispensers. The system controller 30 includes a navigationcontrol 32 which receives global positioning information from a datareceiver 33 and correction data information from a second receiver 34. Auser interface 36 is provided which can include a keyboard or touchscreen, and a display to allow the farmer to monitor the performance ofthe system, obtain feedback information, and reconfigure the systemcontrol as required.

The navigation controller provides information to a product deliverycontroller 38, which information includes the current position of theapplicator vehicle 10, typically in terms of latitudinal andlongitudinal (lat-lon) coordinates. Alternatively, the lat-loncoordinates can be replaced by universal trans-mercatur (UTM)coordinates. A number of algorithms implemented by the product deliverycontroller 38 determines the appropriate prescription based upon theglobal location of the applicator vehicle 10 relative to the digital mapinformation provided to the controller. Control signals 39 are producedby the controller 38 which are fed by way of separate individual signals39_(a-j) to each of the controllers, pumps and motors associated withthe applicator vehicle. In addition, the product delivery controller 38receives sensor signals 40 which are a compilation of a number ofsignals 40_(a-h) from a number of sensors 41_(a-h) associated theproduct dispensing components. These sensor signals can provideinformation concerning the state of the particular product dispensingmechanism (for example, full or empty), of a malfunction of the system,or of actual product quantity dispensed from the particular bin or tank.

As described above, a critical aspect of the invention is the ability tonavigate the applicator vehicle (hereinafter referred to as the unitunder control--UUC). Proper implementation of the agricultural productdelivery prescription requires knowledge of the precise location of theUUC with respect to the acreage being treated. Thus, the digital maprepresenting the acreage A shown in FIG. 1, includes informationconcerning the exact latitudinal and longitudinal coordinates of theacreage and of the treatment prescription areas A_(1-n). Likewise, theexact location of the UUC must be ascertained during application of theprescription products. The mobile navigation controller 32 shown in FIG.2 accomplishes that function.

In the preferred embodiment of the present invention, the globalpositioning system (GPS) is used to provide relatively exact andcontinually updated information concerning the position of the UUC inglobal coordinates. In one aspect of the present invention, adifferential GPS protocol is implemented. It is also known that GPSsignals being received from a number of orbiting satellite are subjectto a number of errors which dilute the navigation accuracy of the mobilenavigation controller 32. It is known that the navigational accuracy ofa GPS receiver is characterized, to at least a first approximation, bymultiplying the satellite range measurement (pseudorange) error timesthe dilution of precision (DOP) satellite geometry factor. Navigationalaccuracy can be improved by decreasing the DOP or by increasing theaccuracy of the pseudorange measurement. In accordance with the presentinvention, it is the pseudorange errors that are sought to be accountedfor.

Pseudorange errors which are common between local receivers aresusceptible to differential treatment. The major common error sourceswhich are subject to this differential treatment include selectiveavailability errors, of up to 30 meters; ionospheric delays, varyingbetween 20-30 meters by day and 3-6 meters by night; troposphericdelays, up to 30 meters; ephemeris errors, typically less than 3 meters;and satellite clock errors, typically less than 3 meters. Selectiveavailability errors are caused by deliberate distortion of the GPSsignals by the U.S. Government to reduce the inherent accuracy of GPSfor security reasons. Ionospheric and tropospheric errors increase asthe separation distance between a reference station and a mobilereceiver, such as mobile navigational controller 32, increase. However,if the distance between these two stations is less than about 500 miles,the total navigation error due to ionospheric and tropospheric delayscan be kept below 5 meters.

In order to remove, or at least greatly minimize, the cumulative effectof each of these common sources of pseudorange error, the presentinvention contemplates a GPS differential reference station, such asstation 45 shown in FIG. 3. This station includes a GPS all-in-viewreceiving apparatus 46, and a correction data link 47 for transmittingcorrected positioning data to the mobile navigation controller 32. TheGIPS receiving apparatus 46 includes an appropriate antenna forreceiving a number of signals transmitted by a Lumber of orbiting spacevehicles, such as satellites A-D. The antenna 46 can be similar to theGPS data receiver 33 connected to the mobile navigation controller 32.The correction data link 47 includes a transmitter capable oftransmitting at a nominal range of 500 miles to the correction datareceiver 34 on the mobile navigator control 32.

The differential reference station also includes a computing means, orcomputer 48, which is used to perform the GPS differential referencecalculations. The location of the GPS reference station 45 is carefullysurveyed to determine its phase center position. The known latitude andlongitude of the station is input at 49 to the computing means 48. Thisknown lat-lon is then used to calculate the GPS pseudorange error. Thecomputing means includes software means for interpreting, latitude,longitude and altitude information received by the GPS receivingapparatus 46 from each of the number of satellites A-D. In particular,the computing means 48 compares the lat-lon information based on thesignals from the space vehicles with the known lat-lon of the referencestation. A correction value is computed which is then communicatedcontinuously and in real-time through the data link 47 to the correctiondata receiver 34 on the mobile navigation controller 32.

A preferred reference station receiver is a multi-channel "all-in-view"receiver with one channel assigned to each visible satellite. Withcurrently-planned satellite constellations of about 21 satellites, abouteight satellites are in view at any given time. Thus, an eight-channelreceiver is desirable. The computing means 48 performs theaforementioned pseudorange error calculations for each satellite inview. A correction value for every in view satellite is then transmittedacross data link 47 to the mobile navigation controller 32 to be used ina manner described below.

Referring now to FIG. 4, a block diagram of the system controller 30 isshown. The system controller 30 as previously described includes acorrection data link receiver 34 and a GPS data receiver 33. The GPSreceiving apparatus 33 can be substantially similar to the referencestation receiving apparatus 46, although the receiving apparatus for themobile unit need not have the same number of channels for themulti-channel receiver. Preferably, the GPS receiving apparatus 33 is afour or more channel receiver for receiving GPS data from at least fourspace vehicles A-D to provide sufficient latitude, longitude andaltitude information. The GPS receiver 33 of the system control 30 ofthe UUC is equipped with circuitry to accept correction data from thecorrection data link 34. The GPS receiving apparatus 33 includessoftware to select appropriate ones of the satellite signals received bythe mobile navigation controller 32. This software selects from theall-in-view satellites available to the mobile GPS receiving apparatus33, which selection is limited to those satellites for which pseudorangecorrection data has been received from the reference station 45. The GPSreceiving apparatus 33 then integrates this correction data with the GPSposition data received from the selected satellites to produce correctedand accurate real-time position information for the UUC.

This corrected lat-lon data is then fed to a GPS interface coprocessor35 which sorts the wide variety of information and messages from the GPSreceiver and stores this information in addressable locations so thatthe computing means 50 of the system controller 30 can access theinformation in a rapid manner over a parallel data bus 51. Theinformation supplied over the data bus 51 from the GPS interfacecoprocessor 35 to the computing means 50 includes the correctedlatitude, longitude and altitude of the vehicle, along with the precisetime and date, and the speed and track over ground of the UUC. All ofthis information is available from the GPS system through the receivingapparatus 33 and coprocessor 35.

The system controller 30 includes a central computing means 50, which ispreferably a microprocessor-based computer. This computer can be placedin the operator compartment of the UUC to provide environmentalprotection for the unit. The microprocessor 50 sends and receivesinformation to and from a number of components. A user or operatorinterface 36 is provided, which is shown in more detail in FIG. 5. Theuser interface allows the operator to monitor the operation of thenavigation system controller as well as to provide instructions to thecontroller. In the preferred embodiment, the user interface 36 includesa color CRT 36a capable of displaying multi-color map information. Theinterface also includes an input device, which in the preferredembodiment is a touch screen display 36b. The touch screen capability ispreferred because the operations that would typically be requested bythe operator are few in number. Alternatively, a separate keyboard canbe provided having only a few keys corresponding to the critical userinterface functions. However, the touch screen allows both the userinput and the display output to be integrated into a single package. Thedisplay screen 36b can be controlled by a graphics coprocessor 37 whichis connected by a parallel bus to the microprocessor computing means 50.

The system controller 30 further includes a solid-state disk drive 52and a solid-state disk emulator 53. The solid-state disk drive 52, whichpreferably uses a removable disk, contains navigation instructions andinformation concerning the specific UUC tasks. This task and navigationinformation is loaded prior to operation of the UUG and can betransported to the UUC via a credit-card size removable memory supportedby the solid state disk drive 52. The solid state disk drive 52preferably is a non-mechanical drive which is environmentally sealed toavoid contamination as the UUC is operated in the field.

The solid state disk emulator 53 is also a non-mechanical unit. Theemulator is not removable from the complete package of the systemcontroller 30, and is preferably enclosed within the housing for themicroprocessor 50. The solid state disk emulator 53 contains all of thestart-up software for the primary microprocessor computing means 50,such as the operating system, application software, and hardware driversfor peripheral computing boards.

The microprocessor central computing means 50 also interfaces with theproduct delivery controller 38, or more specifically a UUC interfacecoprocessor. This interface coprocessor 38 includes serial and paralleldata lines for transmission of data to and from various components ofthe vehicle control electronics, such as controllers 19_(a-f).Information can also be sent back to the central computing means 50 forincorporation into a performance record that is recorded on the solidstate disk drive.

The system controller 30, and principally the microprocessor computingmeans 50, implements a number of resident software routines forperforming the navigation said prescription controlling functions. Thedetails of these routines, along with the details of the procedureimplemented by the computing means 50, is described herein withreference to the flow charts shown in the figures. Referring first tothe basic flow chart shown in FIG. 6, the main procedure is implementedby the microprocessor computing means 50 to control the flow of theprogram by asserting calls to a number of subroutines. A firstsubroutine call 60 is to initialize the peripheral computing boards,such as a board for the coprocessor 37, an interfacing controller boardfor the GPS receiving apparatus 33, and an embedded controller forinterfacing as part of the UUC interface coprocessor 38. Program flowproceeds from the computing board initialization procedure subroutine 60to the mass storage loading procedure subroutine 61. Details of thissubroutine 61 are shown in the flow chart of FIG. 7.

In the mass storage loading subroutine 61, data is read from a slowernon-volatile memory, such as from the solid state disk drive 52, andtransferred to a more readily accessible random access memory (RAM)contained within the microprocessor computing means 50. In the remainingsteps of the subroutine 61, specific default data is loaded into RAMwhich corresponds to various performance and map display informationessential to the operation of the system controller 30. In the firststep of the subroutine, a default map scale value is loaded in step 61a.This value represents a coefficient by which the size of the mapdisplayed on the user interface display 36a will be magnified.

A typical map M is shown on the display 36a in FIG. 5. In the display,each pixel of the screen represents the smallest discernible incrementof information conveyed when the map scale value is at 1.0. If thisscale value is increased to some multiple of one, each pixel of thegraphics screen will represent a multiple of that particular increment.For example, if the resolution o f the data received from the CPSinterface coprocessor 35 is 0.001 minutes (in lat-lon coordinates) andthe scale value is 1.0, then each pixel on the display screen 36arepresents 0.001 minutes latitude or longitude. However, if the scalingfactor is increased to a value if 2.0 for example, each pixel wouldrepresent 0.001/2.0 or 0.0005 minutes latitude or longitude. In otherwords, increasing the map scale value increases the resolution of thedisplay on screen 36a. In the preferred embodiment, the default mapscale value is 1.0 so that each pixel on the screen 36a corresponds tothe actual resolution of the data received from tile CPS coprocessor 35.

In the next step 6b, a default delay factor is loaded into RAM. Thisdelay factor represents the distance required for the UUC to respond toa change in commands from th e UUC interface coprocessor 38. Forinstance, if the system controller 30 in implementing a particularprescription determines that a change in the amount of product in bin11a (see FIG. 2) is required, it is known that product fed from bin 11aat a new feed rate takes a certain amount of time to travel along theconveyor 20 and reach the rotary spreader 15 at the new rate. Thus, thisdelay factor represents the distance over ground in which it isanticipated that the UUC will be able to respond following a change incommands.

This delay factor is illustrated with reference to FIG. 5. Inparticular, in the center of the display screen 36a is a pair ofrectangular symbols representing the unit under control (UtJC). Thelowermost symbol 62 in black corresponds to the present known positionof the UUC. The symbol 63 in white represents the predicted position ofthe UUC as a function of the delay factor, the course over ground andthe speed over ground of the UUC. Thus, as the system controller 30implements the particular prescription, when the predicted positionsymbol 63 reaches a particular change in prescription, themicroprocessor 50 calculates the change in prescription and transmitsthat information to the appropriate controller in the applicator vehicle10, with the understanding that the product mixture change will reachthe rotary spreader 15 by the time the actual position symbol 62 of theUUC reaches the then current position of the predicted symbol 63.

By way of a specific example, if it is shown that the applicator vehicle10 requires 5 seconds to activate a change in prescription or change inproduct mixture, the distance between the two symbols 62 and 63represents the distance traveled by the UUC at its known current speedover ground over that 5-second time delay. Once the predicted positionsymbol 63 reaches a location on the map M corresponding to the change inprescription, the system controller 30 generates signals transmitted tothe various product controllers on the applicator vehicle so that withinthat 5-second time delay, the new prescription will have reached therotary spreader 15. It should be understood that the actual physicaldistance between the current UUC symbol 62 and the predicted UUC symbol63 will vary for a fixed known time delay value based upon the actualspeed over ground of the vehicle. As the vehicle moves faster, thedistance separating the two symbols on the screen 36a will increase, andconversely as the speed decreases.

In the next step 61c of the mass storage subroutine 61, a default valueof the operating width of the UUC is entered. This value corresponds tothe effective width at which the rotary spreader 15 can dispense theagricultural products from the applicator vehicle. The width of the UUCis represented by the width of the symbols 62 and 63. The graphicscoprocessor 37 adjusts the width of the symbol in relation to the scaleof the map so that the symbol represents actual coverage over theacreage being treated. In a typical circumstance, the actual effectivewidth of the UUC will vary depending upon the type of agriculturalproduct being applied and the manner in which the product is applied.For instance, the rotary spreader 15 shown in FIG. 2 may be replaced bya single spreader bar of a predetermined width. Moreover, the effectiveoperating width of the UUC may vary as the density of agriculturalproduct to be applied is varied.

With respect to the product density, it is known that certain dryproducts may vary in compaction ratio due to the ambient humidity. Inother words, under higher humidity conditions, the dry product maybecome more compacted in the UUC hoppers. This higher compaction canlead to an effective product density different from what may have beenanticipated. Thus, the present invention further contemplates softwarethat generates a scaled product density value that compensates for thecompaction ratio. A default value for the compaction ratio can beentered during the subroutine 61 in which the default value is a knownvalue at standard temperature, atmospheric pressure and humidity.

Referring again to FIG. 7, in the next step 61d of the subroutine 61 thenumber of layers to be read is identified. In accordance with thepresent invention, the map used by the system controller 30 to implementthe agricultural product prescription is represented by a number oflayers. Each layer corresponds to the prescription application map for adifferent product. For instance, in the applicator vehicle 10, if eachbin 11a-f, each liquid tank 12a-b and each accessory bin 3a-b is filledwith product to be applied to the acreage, then up to ten differentproducts can be applied to the acreage. Each product may have adifferent prescription for application depending upon the soil contentand the crops grown in the soil. Each layer of the map corresponds to asingle product dispensing mechanism that is to be controlled by thesystem controller 30. The preferred embodiment contemplates up to tenlayers, of which only six layer maps 65a-65f are shown in FIG. 8. Eachlayer corresponds to a different agricultural product to be dispensedonto the acreage.

The present invention implements a protocol that makes the mostefficient use possible of the limited memory of the system controller onboard the UUC. This protocol provides for RAM storage of informationrequired for making a two-dimensional digital drawing of each map layer,without storing the entire map layer represented by thousands of pixels(and therefore bytes) of information. As described more fully herein,only the vertices of a number of zones that comprise a given layer arestored in RAM. Software within the system controller 30 then uses thisstored vertices information to "draw" each map layer as that layer isbeing processed to extract the product prescription informationcontained therein. Once a layer map has been "drawn" and theprescription information extracted for the global coordinates of theUUC, the layer can be displayed on display 36a. The operator may selecta different layer, corresponding to a different product prescription, tobe displayed using the touch screen user interface 36b, which layer canbe displayed once it has been drawn and processed in accordance with theprocedure described more fully herein. Borrowing the parlance of thecomputer graphics art, as each layer is being processed it is beingdrawn onto the "active" invisible page. A layer can be called by the UUCoperator onto a "non-active" visible page for visual display.

In the next step, 61e of subroutine 61, a related step is performed inwhich the number of zones per layer is loaded into RAM. Referring toFIG. 8, it can be seen that the layer 65a includes four regions 66a-66dhaving different colors or shadings. Each of these colors, or moreappropriately zones in accordance with the present invention, representsa level of activity to be conveyed to the respective product controllermechanism in the applicator vehicle 10. Reference to the level ofactivity simply means the quantity or rate of feed of the particularagricultural product to the rotary spreader 15. Thus, zone 66a maycorrespond to a product feed rate of 5 units per acre, while the nextadjacent zone 66b may represent a feed rate of 10 units per acre. As theUUC from zone to zone, the system controller 30 interprets theinformation within that zone and sends a corresponding signal to thecontrollers of the applicator vehicle to effect a change in product feedquantities or feed rates.

In the preferred embodiment of the invention, up to ten layers having upto fifty zones per layer can be stored in a data base within the systemcontroller RAM. Thus, the steps 61d and 61e produce a two-dimensionalmatrix of product activity levels as a function of the number of zonesand the number of layers. A representative matrix of data stored in theRAM is shown in FIG. 9. For simplicity, only six of the ten possiblelayers (corresponding to the six product bins 11a-11f shown in FIG. 1)and ten of the fifty possible zones are represented. The levels ofactivity for each of the products are represented by L1-L10 , with L1corresponding to the lowest level of activity and L10 corresponding tothe highest. Columns of the matrix represent the products to bedispensed. In this instance only four products are dispensed, so thatthe columns of the matrix corresponding to the fifth and sixth layers,or products, are empty. Each row of the matrix corresponds to the numberof zones representing the levels of activities for each product. Again,as with the map layers, not all zones need be filled with data andrepresented on the digital map. For example, for the first product onlyfour activity zones are identified, which corresponds to the four zones66a-66d for layer 65a shown in FIG. 8. It can be seen that in the firstzone, the level of activity is at the lowest level L1, but the activityincreases to level L3 in the next zone. Likewise, the second layercorresponding to a second product includes only two levels of activityand consequently only two zones are represented on its corresponding map65b in FIG. 8. The third product, represented by a third layer of themap, includes levels of activity in each of the ten zones which varybetween each zone.

Referring back to FIG. 7, in the next step 61f of the subroutine 61values are loaded into RAM corresponding to the colors assigned to eachzone within each layer. It is understood that the nomenclature "color"is not necessarily intended to be used in a visual or graphic sense.Instead, identification of different colors for each zone within a layeris intended to suggest a protocol for representing universal levels ofactivity. In other words, referring back to FIG. 9, the lowest level ofactivity for product 1, L1, may not be the same as the lowest level ofactivity for product 3. For instance, it ran be contemplated the product1 may normally be spread or dispensed at 10 levels ranging from 1 unitper acre to 10 units per acre, while a second product may range inactivity level from 50 units per acre to 140 units per acre. The datastored in the RAM matrix depicted in FIG. 9 represents control data fedto the various product dispensing controllers. Consequently, a universalscheme is required for representing actual levels of activity for thedifferent products being dispensed. In the present invention, thisuniversal scheme is implemented by assigning different "colors" to eachzone of each layer. For example, the lowest level of activity forproduct 1 can be represented by the color green while the lowest levelof activity for product 3 can be represented by the color red. (Again,it is understood that the computer does not understand the physicalsense of color.) The term "color" is used as a shorthand notation to adda third dimension to the matrix of FIG. 9. However, similar colors canbe used to represent the same levels of activity between layers.Likewise, the same colors can be used to correspond to different levelsof activity across different product layers.

Thus, in step 61f of the subroutine 61, the values for the color foreach zone for each layer are loaded into RAM. In the preferredembodiment, up to ten colors are utilized. In the next step 61g, atranslation table is also loaded into RAM which correlates a particularcolor corresponding to a zone in a given layer, to a specific outputmagnitude provided to the product controllers in the UUC or applicatorvehicle 10. This translation table operates simply as a look-up tableonce the microprocessor computing means 50 has extracted a particularcolor from the layer/zone matrix in RAM. In order to interface with16-bit product delivery controllers, each value in the translation tablecan be a 16 bit value.

The last two steps 61h and 61i of the subroutine 61 concern therepresentation of the different zones in each layer of the map. In thefirst step, the number of vertices per zone per layer are loaded intoRAM. In accordance with the present invention, each zone is defined asthe area within a polygon. The complexity of that polygon can vary as afunction of the number of vertices. For example, referring again to FIG.8, the zone 66a of the first layer 65a of the map can be defined by anumber of vertices 67. The vertices define the contour of the zone 66a.It is understood, of course, that the greater degree of convolution orcurvature of the perimeter of the zone polygon determines the number ofvertices necessary to define the polygon. In addition, the amount ofcurvature is limited by the resolution of the navigation information, orlat-lon data, available to the system controller 30. In step 61i, theactual latitude-longitude coordinates for each of the vertices 67 isdefined for each zone and for each layer. The amount of storage requiredfor the data loaded in step 61h and 61i depends upon the degree oflat-lon resolution available from the GPS system and the amount ofconvolutions of the polygon representing the various zones in eachlayer.

Returning again to FIG. 6, following completion of the mass storageloading procedure, control of the main procedure routine passes to theprogram variable and its initialization subroutine of step 70. In thisstep all global variables and graphics parameters are given initialvalues. The global variables include variables which are used by all theprocedures. The graphic parameters include values corresponding to whichlayer of the map is to be active and which is to be displayed. Inaddition, any modifiable look-up tables are also initialized.

Thus far, all the subroutines of the main procedure have been toinitialize the routines of the system controller 30 in preparation forreal-time operation of the navigation control and prescriptiondispensing features of the invention. The real-time operation of thesoftware in the system controller 30 performs a number of functions in aprocedure loop 71. In the first step of the procedure loop, step 72, theGPS interface coprocessor 35 (FIG. 4) is interrogated by themicroprocessor computing means 50. In this subroutine 72, detailed ornon-detailed GPS information is transmitted from the coprocessor intooperating RAM within the microprocessor computing means 50 for use bythe remaining procedures. Information obtained from the interfacecoprocessor (which information is obtained upstream from the GPS systemitself) can include information concerning the status of the GPSsatellites, the position of the mobile unit under control, and speed andheading data. The status information can include messages concerning thestatus of the receiver 33, the number of satellites visible and thenumber of satellites being tracked by the mobile navigation controller32. The status information can also include the real time since the lastnavigation procedure was performed by the system controller 30.

The position information can include the GPS time, latitude, longitude,altitude and position source information. The speed and heading data caninclude information concerning the course over ground as well as thespeed over ground of the UUC 10. The data provided from the GPSinterface coprocessor 35 to the microprocessor computing means 50 can beviewed by the operator of the UUC as desired or required.

More detailed information, which is also available from the GPS system,can be read by the microprocessor 50 and made available to the operatorthrough the user interface 36. This information includes the status,position and speed/heading data available under the normal non-detailedGPS interrogation, as well as several other messages providing moredetailed information concerning the GPS satellite system itself. Thisinformation can include the dilution messages concerning the dilution ofprecision, mode data, satellite health status and signal strength,position of the satellites, software configuration of the GPS receiverand time recovery results. Selection of the non-detailed GPS statusinformation speeds up the throughput through the system controller 30.However, there may be instances when more detailed informationconcerning the GPS system and satellites would be desired. If this isthe case, the GPS input procedure 72 provides means for requestingdetailed information that has already been stored in the GPS interfacecoprocessor 35 and transmitting this information to the centralmicroprocessor computing means 50.

Once the current GPS data has been stored within RAM in themicroprocessor 50, the operator interface is interrogated to determinewhether a manual data entry has been made. In the case of a touchscreen, the touch screen is interrogated to determine whether the screenhas been touched at valid coordinates defined by a specific menu table.If so, then the display on the screen is changed to the particular menuand that menu is made the active menu for further user input. Once aspecific function has been called out by the user on the touch screen,that function is performed by the microprocessor 50 according tosoftware associated with that function.

The next step of the main procedure is a decision block 75 in which itis determined whether the GPS data received in the GPS input procedure72 has changed from the data received in the previous pass through loop71. In other words, the main procedure implemented by the microprocessor50 looks to see whether the UUC has moved--that is if its latitude andlongitude has changed. If the data has changed, or if the UUC has movedsince the GPS coprocessor was last interrogated, the map generationprocedure of subroutine 76 is called to produce the digital maprepresenting the current location of the UUC with respect to the variousprescription layers.

Details of the map generation procedure 76 are shown in FIG. 10. Duringthis map generation procedure, the microprocessor computing means 50"draws" each layer of the map and interrogates each layer to extract therequired information from the layer. In accordance with the presentinvention it is understood that when the computing means 50 "draws" alayer it reads the vertices information for that layer to determine thelocation of the several zones of the layer, and then assigns each pixelof the layer map to an appropriate zone based upon its location withinthe layer map. A layer map being interrogated in a step of the mapgeneration procedure 76 is drawn onto the "active" invisible page ingraphics RAM and is referred to as the active layer. The layer beingdisplayed for viewing by the UUC operator is maintained on an "inactive"visible page of the graphics RAM. Software within the graphicscoprocessor conducts a "page flip" to switch the inactive visible pagewith the active invisible page to allow interrogation of the layerpreviously displayed to the UUC operator.

At the beginning of the map generation procedure, a counter is set toone greater than the value of the layer that has been requested by theoperator as the layer to be displayed. The remaining layers of theprescription map will be sequentially processed and interrogated. Shecounter is incremented through each of the number of layers and isreduced to the lowest numbered layer if it exceeds the stored value forthe maximum number of layers to be processed. Once the counter cycles tothe user requested layer and that layer is processed, control is passedout of the layer interrogation and processing loop.

After the layer counter is initialized or incremented, the softwarewithin computing means 50 draws the layer indicated by the counter. Aspreviously discussed, the layer is comprised of a multitude of polygonsdefined by vertices translated from latitude/longitude data to screencoordinates. The center of the screen is defined as the location of theUUC or the current GPS coordinates. This drawing step initially takesplace in the active invisible page of graphics RAM and is not displayedto the operator.

In the next step of the routine 76, the layer is interrogated todetermine the activity levels for the particular component. Inparticular, the microprocessor 50 interrogates the pixel in advance ofthe current latitude and longitude by a distance determined by the delaycoefficient (corresponding to the default delay factor set in step 61bof FIG. 7), the speed over ground and the course over ground of the UUCas determined by the GPS data. Specifically, the map generationprocedure interrogates the pixel directly beneath the predicted positionsymbol 63 shown on the screen in FIG. 5. The value of this pixel isstored in RAM for subsequent use by the next step of the main procedurein which data is output to the unit under control.

A decision block 76a determines whether all of the layers have beenprocessed and interrogated. If not, control returns by loop 76b to drawand interrogate the next sequential layer. On the other hand, once thecounter reaches the number of the user requested layer, control passesfrom the decision block 76a to the step 76c of the map generationsubroutine 76. In this step a black path the width of the vehicle isdrawn over the area previously operated upon. More specifically, a newpolygon is created which defines the area formed between the lastposition update and the current position update corresponding to thevehicle coverage width. This solid color denotes that the vehicle hasalready traveled over that particular location. This solid color, orblack, polygon is stored in memory and is displayed on the displayedlayer so that the operator can determine regions of the agriculturalfield that has already been serviced. In the next step, the pixel at thecurrent latitude and longitude is again interrogated and the soliddirectional symbol corresponding to the present position of the vehicleis drawn at that location. An outline vehicle symbol, such as vehiclesymbol 63, is also drawn in advance of the solid symbol corresponding tothe projected position of the UUC given the delay factor and the speedover ground.

In the final step of the map generation procedure 76, the activegraphics page, or the map layer being operated on by the procedure, ismade the visible page displayed on display 36a for viewing by theoperator. The previous visible page then becomes the new active page ingraphics RAM. When the map generation procedure has been completed, thevalues of the pixels for each map layer at the predicted position of theUUC (icon symbol 63 in FIG. 5) are stored in RAM waiting to betransmitted to the UUC interface coprocessor.

At this point, control is then returned to the main procedure in whichthe next step 77 is executed to output control information to the UUCinterface coprocessor 38. In this procedure 77, the last interrogatedpixel is reviewed to determine whether it is black or has a differentcolor. If it is not black, then the particular color or output valuespecified by the color is passed to the translation table defined instep 61g (FIG. 7). If that pixel's color is black, the color has beenchanged to black in a previous path through the loop 71 because the UUChas already traveled over that particular location. In this instance, apredetermined value, such as a null or zero (0) value, is substitutedfor the previous value of the pixels interrogated for each layer. Anappropriate control signal is then extracted from that translation tableand passed to the unit under control through the UUC coprocessor 38. Inthe case of a null or zero value, the control signal obtained from thetranslation table can signify an inactive state for the several productdistributors.

In the final step of the map generation procedure loop step 78, feedbackis received from the UUC. This feedback can include informationconcerning the performance of the various product distributors of thisprinting vehicle 10. This information can then be recorded onto a massstorage device as a record of the events which have occurred during thecourse of operation of the UUC. In addition, the current position,course and speed of the UUC can be stored as a further record of events.Following this feedback procedure 78, control is passed through loop 71back up to the GPS input procedure 72 to update the current position ofthe UUC.

The map generation procedure 76 implemented by the microprocessor 50 aswell as the graphics coprocessor 37 cooperate to provide several mapfeatures that are beneficial and useful to the operator. For instance,the present invention contemplates a moving map display, such asdepicted in FIG. 11. In FIG. 11, the map position at two instants oftime is depicted. At the first time, time 1 on the left side of FIG. 11,the entire field map is shown with only a part of the map being actuallydisplayed on the screen. It is understood that the entire field mapcould be displayed on the screen if the display field was increased insize using a zoom capability. However, the normal size of anagricultural field would be too large to fit in a single display andstill have a meaningful display for the operator. Thus, as shown in thefigure at time 1, only a portion of any prescription map will bedisplayed on the screen 36a. At a later instant in time, time 2, it canbe seen that the entire map has shifted down in the screen relative tothe symbol 62 for the vehicle.

Two additional features of the present invention are depicted in FIG.11. First, a black strip 79 can be seen trailing each of the UUC symbols62. As discussed with respect to the map generation procedure subroutine(FIG. 10), the black strip represents previously covered area of theagricultural tract. As can be seen in the updated map at time 2, theblack strip extends beyond the portion of the map actually displayed.This is an indication that the microprocessor 50 maintains a "picture"of the map in RAM, which picture will include designation of the colorblack for the pixels previously covered by the path of the UUC.

Another feature of the invention concerns the manner in which each ofthe pixels within a given polygon are colored either on the screen or ininternal memory. In previous devices, such as the device in the SoilteqU.S. Pat. No. 4,630,773 discussed above, each pixel of a given map isassigned a specific value and retains that value throughout an entireoperation of the applicator vehicle. Thus, as the map is translated orrotated on the display, or as the vehicle or UUC travels in a path overthe map in memory, each pixel must be treated separately, either rotatedor translated. This feature of the prior art devices makes the mapgeneration and operation procedures extremely cumbersonme because everypixel must be accounted for at every step of the procedure. Not only isthis prior approach very memory intensive (a 250×250 array of pixelswill include 62,500 pixels) but any moving map function is very slow andgenerally incapable of the quick response expected by the operator ofthe UUC.

To alleviate these problems of the prior art, the present invention usesthe polygon approach to defining areas in its moving maps. As previouslydiscussed, in this polygon approach, specific treatment areas aredefined simply by vertices of a polygon. As a polygon on the moving mapis translated or rotated, only the vertices are moved. Once the polygonhas been moved to its current position, each of the pixels within thepolygon is assigned the appropriate color associated with the particularpolygon or treatment zone. The translation and rotation of the polygonsor zones of the map is illustrated in FIGS. 12a and 12b.

In the first figure, FIG. 12A, the polygon is translated whilemaintaining or UUC's current position in the center of the screen.According to the translation algorithm, the difference in actuallatitude and longitude between the current position of the UUC and thefixed latitude and longitude of the vertex is determined. These deltalatitude and longitude values are converted into the number of screenpixels that these distances would be represented by were they to bedisplayed on the screen. Tie delta pixel values are then multiplied by ascaling value in order to increase or decrease the resolution of thesystem, and therefore the display, as required. With the scaled deltapixel (delta latitude and longitude) values, these values are added toan offset value which defines the physical center of the screen basedupon the particular resolution of the screen. For instance, if thescreen resolution is 640×480 pixels, as in the preferred embodiment,then an offset of 320×240 pixels would locate the center of the screen.The scaled delta pixel values are then measured from that zero point toproperly locate the vertex, and consequently the fully formed polygon atits new location on the screen.

The rotation of a polygon, or prescription zone, is accomplished inaccordance with the procedure illustrated in FIG. 12B. Once the polygonhas been translated (or panned), it can be rotated about the center ofthe screen position at which the UUC symbol is drawn. In order toascertain the proper rotation, the vehicle heading is ascertained fromthe GPS data provided to the microprocessor 50 by the GPS interfacecoprocessor 35. This heading represents an angle of rotation about thecenter of the graphics screen. The new X and Y positions of thevertices, as defined in pixels on the graphics screen, can be calculatedaccording to the following equations:

    x(new)=(x(old)-xctr)*cos(hdg)-(y(old)-yctr)*sin(hdg)+xctr

    y(new)=(x(old)-xctr)*sin(hdg)+(y(old)-yctr)*cos(hdg)+yctr

where "hdg" is the vehicle heading, "xctr" and "yctr" are the physicallocations in the center of the graphics screen and "x(old)" and "y(old)"are the original positions of the particular vertex on the graphicsscreen.

Application of these two equations results in the calculation of new Xand Y locations for the vertex on the graphics screen. Each vertex isrotated in the same manner and once all the vertices have been rotated,the pixels are filled in with the appropriate color defined by thespecific polygon/zone. The rotation of these particular polygons orzones of a map is typically done in order to keep the vehicle symbolpointing upward in the same direction on the screen. However, if it isdesired by the operator, the vehicle symbol itself can be rotated whilethe remainder of the map is simply translated as the vehicle movesthrough the agricultural field. The same polygon rotational algorithmdescribed above can be used to rotate the polygon used as a symbol torepresent the UUC. This particular feature may be beneficial if theoperator desires to maintain a specific compass orientation for thescreen display.

As discussed above, the user interface 36 includes a touch screen userinput portion 36b. The details of one specific embodiment of the touchscreen are shown in FIGS. 13A and 13B. In FIG. 13A, a typical touchscreen display is shown which includes features for changing the widthof the UUC symbol, and changing the magnification of the actual displayshown on the screen. In addition, delay buttons allow the operator todeliberately change the delay factor as represented by the distancebetween the actual position symbol 62 and the predicted position symbol63. A number of screen switch positions correspond to each of the sixbins of product that can be serviced by the present invention. Theoperator can call up the particular layer of map corresponding to one ofthe six bins shown on the screen. Finally, the bottom bar on theparticular display in FIG. 13A allows the operator to access a secondmenu for displaying the GPS data. The second menu is shown in FIG. 13B.The touch screen feature of the user interface 36 provides a relativelysimple means for the operator to control the operation of the systemcontroller 30 and obtain up-to-date real time information concerning theperformance of the entire system.

FIG. 14A shows the zoom capability of the present invention assuming theoperator has pressed the zoom (+) symbol on the touch screen display ofFIG. 13A, it can be seen that with the zoom capability, the size of theUUC symbol is also increased because the actual operating width of theUUC assumes a greater portion of the region of the agricultural fielddisplayed on the screen. In FIG. 14B, the feature previously describedin which the UUC symbol is rotated is depicted. In this display, the UUCis shown heading toward the agricultural field in the upper right cornerof the display. This provides a visual navigation feature for theoperator as he drives the applicator vehicle from the storage facilityto the acreage to be farmed.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

While the preferred embodiment of the present invention concerns amethod and apparatus for controlling an applicator vehicle forprescription farming, the invention contemplates application in otherfields and endeavors. The method and apparatus can be implemented on anapparatus having a number of functional components, each capable ofcontrollable levels or manners of activity. Control of the activity ofthese functional components can be based upon the geographic position ofthe apparatus. For example, method and apparatus in accordance with thepresent invention can be implemented on a crop spraying airplane. Thepresent invention can also have application in controlling digging andtunneling apparatus where the level and manner of activity of thefunctional components can be based upon different soil or rockcompositions at different geographic locations.

What is claimed is:
 1. A prescription farming control system for use incontrolling product delivery mechanisms mounted on an applicatorvehicle, the delivery mechanisms operable to deliver product to spreadermechanisms for spreading products over an agricultural field, each ofthe product delivery mechanisms having a device controller whichcontrols the rate of operation of the corresponding delivery mechanismin response to a control signal derived in accordance with aprescription for the field, the control system comprising:means forstoring in a digital memory information defiling a digital maprepresentative of the prescription for the field, the map being definedby a number of layers, each layer corresponding to one of the productdelivery mechanisms, and each layer including a number of zones, eachzone corresponding to a rate of application of the corresponding productin accordance with the prescription for the field at a plurality ofglobal positions within the zone; means for storing a data tablecontaining control signal values for each of said number of zones ineach of said number of layers, said control signal values beingindicative of the rate of application of the product associated with acorresponding layer at positions of the vehicle within a correspondingzone; navigation means for determining the current position of theapplicator vehicle on the agricultural field in global coordinates asthe vehicle moves over the field; and means for transmitting, to eachdevice controller, selected ones of said control signal valuescorresponding to said zone of each layer for which the determinedcurrent position of the vehicle corresponds to one of said plurality ofglobal positions within the zone.
 2. The prescription farming controlsystem of claim 1, wherein said navigation means includes:a firstreceiver mounted on the applicator vehicle for receiving positioningdata from a number of global positioning system (GPS) satellites; asecond receiver mounted on the applicator vehicle for receivingpseudorange correction data from a fixed position ground station; andmeans for operating on said positioning data and said pseudorangecorrection data to generate corrected global coordinates for the currentposition of the applicator vehicle.
 3. The prescription farming controlsystem of claim 2, wherein:said first receiver is an all-in-viewreceiver; said fixed position ground station includes:an thirdall-in-view receiver; and means for calculating pseudorange correctiondata for all satellites in view of said third receiver; and said meansfor operating includes means for selecting position data from several ofall satellites in view of said first receiver for which pseudorangecorrection data is received from said ground station.
 4. Theprescription farming control system of claim 1, wherein:said means forstoring information includes information corresponding to the globalposition of plurality of vertices, said plurality of vertices definingsaid number of zones for each layer; and said means for transmittingincludes;graphics processor means having a graphics memory and means fordigitally drawing each of said layers sequentially in said graphicsmemory by assigning a plurality of pixels to each of said number ofzones within each sequential layer; means for interrogating the one ofsaid plurality of pixels in each layer corresponding to the currentposition of the vehicle to determine the zone to which said one pixel isassigned; and means for reading said data table to obtain a controlsignal value corresponding to said zone within each layer to which saidone pixel is assigned.
 5. The prescription farming control system ofclaim 1, further comprising:a display monitor mounted in the applicatorvehicle; means for producing a graphic image of an operator selectableone of said number of layers of said digital map on said monitor; andmeans for displaying a symbol representing the vehicle at a location onsaid graphic image corresponding to the absolute position of the vehiclerelative to the field.
 6. The prescription farming control system ofclaim 5, wherein said means for displaying a symbol of the vehicleincludes means for varying the width of said symbol relative to saidgraphic image in relation to the effective width of coverage of thespreading mechanisms of the vehicle.
 7. The prescription farming controlsystem of claim 1, wherein said means for storing information and saidmeans for storing a data table each includes a computer memory havingstorage locations for information related to up to ten (10) layers, eachhaving up to fifty (50) zones.
 8. The prescription farming controlsystem of claim 5, wherein said means for displaying a symbolrepresenting the vehicle includesmeans for producing an egocentricdisplay; and means for translating and rotating said graphic image ofthe selected layer relative to said egocentric vehicle display inrelation to movement of the vehicle through the field.
 9. Theprescription farming control system of claim 4, further comprising:adisplay monitor mounted in the applicator vehicle; means for producing agraphic image of an operator selectable one of said number of layers ofsaid digital map on said monitor; and means for displaying a symbolrepresenting the vehicle at a location on said graphic imagecorresponding to the absolute position of the vehicle relative to thefield.
 10. The prescription farming control system of claim 9, whereinsaid means for displaying a symbol representing the vehicleincludesmeans for producing an egocentric display; and means fortranslating and rotating said graphic image of the selected layerrelative to said egocentric vehicle display in relation to movement ofthe vehicle through the field, said means including means fortranslating and rotating said vertices of each of said zones of thedisplayed layer.
 11. The prescription farming control system of claim 1,further comprising means for preventing the application of a productwhen the current position of the vehicle is within a portion of thefield over which the vehicle has already traveled.
 12. The prescriptionfarming control system of claim 11, wherein said means for preventingincludes:means for modifying control signal values stored in said datatable for each of said layers associated with the global coordinates ofsaid portion of the field, wherein said modified control signal valuescorrespond to an inactive state of the corresponding device controller.13. A control system for use in controlling functional components of avehicle operable to change its global position, each of the functionalcomponents capable of controllable levels of activity, each functionalcomponent having device controller which controls the operation of thecorresponding component in response to a control signal derived inaccordance with a predetermined prescription of operation over a tractof land, the control system comprising:means for storing in a digitalmemory information defining a digital map representative of theprescription over the tract of land, the map being defined by a numberof layers, each layer corresponding to one of the functional components,and each layer including a number of zones, each zone corresponding to alevel of activity of the corresponding component in accordance with theprescription for the tract of land at a plurality of global positionswithin the zone; means for storing a data table containing controlsignal values for each of said number of zones in each of said number oflayers, said control signal values being indicative of the level ofactivity of the functional component associated with a correspondinglayer at positions of the vehicle within a corresponding zone;navigation means for determining the current position of the vehicle onthe tract of land in global coordinates as the vehicle moves over thetract; and means for transmitting, to each device controller, selectedones of said control signal values corresponding to said zone of eachlayer for which the determined current position of the vehiclecorresponds to one of said plurality of global positions within thezone.
 14. A prescription farming control system for use in controllingproduct delivery mechanisms mounted on an applicator vehicle, thedelivery mechanisms operable to deliver product to spreader mechanismsfor spreading products over an agricultural field, each of the productdelivery mechanisms having a device controller which controls the rateof operation of the corresponding delivery mechanism in response to acontrol signal derived in accordance with a prescription for the field,the control system comprising:means for storing in a digital memoryinformation defining the rate of operation of each of the deliverymechanisms at each of a plurality of global positions within theagricultural field; a graphics processor having;a graphics memory withan active invisible page and an inactive visible page; means fordigitally drawing a layer map corresponding to a user-selected one ofthe delivery mechanisms on said inactive page, and for visuallydisplaying said layer map of said inactive page; means for digitallydrawing on said active page a layer map sequentially corresponding tothe remaining ones of the delivery mechanisms; wherein each layer mapincludes information indicative of the rate of operation of thecorresponding mechanism; navigation means for determining the currentposition of the applicator vehicle on the agricultural field in globalcoordinates as the vehicle moves over the field; means for sequentiallyinterrogating each layer map as it is drawn on said active page to readsaid information at a location on said each layer map corresponding tothe determined current position of the applicator vehicle and generatinga control signal value in relation to the rate of operation of thedelivery mechanism corresponding to said location on each said layermap; and means for transmitting control signals to each of the devicecontrollers based upon said control signal value obtained from each saidlayer map.
 15. The prescription farming control system of claim 1,wherein:said means for storing information includes informationcorresponding to the global position of a plurality of vertices, saidplurality of vertices defining said number of zones for each layer; andsaid means for transmitting includes; processor means for determining ifsaid current position of the applicator vehicle is within a particularone of said number of zones; and means for reading said data table toobtain a control signal value corresponding to said particular zonewithin each layer.
 16. The prescription farming control system of claim13, wherein:said means for storing information includes informationcorresponding to the global position of a plurality of vertices, saidplurality of vertices defining said number of zones for each layer; andsaid means for transmitting includes; processor means for determining ifsaid current position of the applicator vehicle is within a particularone of said number of zones; and means for reading said data table toobtain a control signal value corresponding to said particular zonewithin each layer.